问题：如题，百度地图API 在使用点聚合时，如果放大、缩小或移动地图时，添加的文字标签(label)会消失。

原因：API代码中的map.removeOverlay(marker)，在这句话执行的时候，会自动将marker.label =null；

解决：在每次removeOverlay之前先获取到label，方法为getLabel，removeOverlay之后再设置label，方法为setLabel。

完整的代码为将http://api.map.baidu.com/library/MarkerClusterer/1.2/src/MarkerClusterer_min.js的代码完全替换为下列代码：

var BMapLib = window.BMapLib = BMapLib || {};

(function() {

var getExtendedBounds = function(map, bounds, gridSize) {

bounds = cutBoundsInRange(bounds);

var pixelNE = map.pointToPixel(bounds.getNorthEast());

var pixelSW = map.pointToPixel(bounds.getSouthWest());

pixelNE.x += gridSize;

pixelNE.y -= gridSize;

pixelSW.x -= gridSize;

pixelSW.y += gridSize;

var newNE = map.pixelToPoint(pixelNE);

var newSW = map.pixelToPoint(pixelSW);

return new BMap.Bounds(newSW, newNE)

};

var cutBoundsInRange = function(bounds) {

var maxX = getRange(bounds.getNorthEast().lng, -180, 180);

var minX = getRange(bounds.getSouthWest().lng, -180, 180);

var maxY = getRange(bounds.getNorthEast().lat, -74, 74);

var minY = getRange(bounds.getSouthWest().lat, -74, 74);

return new BMap.Bounds(new BMap.Point(minX, minY), new BMap.Point(maxX, maxY))

};

var getRange = function(i, mix, max) {

mix && (i = Math.max(i, mix));

max && (i = Math.min(i, max));

return i

};

var isArray = function(source) {

return '[object Array]' === Object.prototype.toString.call(source)

};

var indexOf = function(item, source) {

var index = -1;

if (isArray(source)) {

if (source.indexOf) {

index = source.indexOf(item)

} else {

for (var i = 0,

m; m = source[i]; i++) {

if (m === item) {

index = i;

break

}

}

}

}

return index

};

var MarkerClusterer = BMapLib.MarkerClusterer = function(map, options) {

if (!map) {

return

}

this._map = map;

this._markers = [];

this._clusters = [];

var opts = options || {};

this._gridSize = opts["gridSize"] || 60;

this._maxZoom = opts["maxZoom"] || 18;

this._minClusterSize = opts["minClusterSize"] || 2;

this._isAverageCenter = false;

if (opts['isAverageCenter'] != undefined) {

this._isAverageCenter = opts['isAverageCenter']

}

this._styles = opts["styles"] || [];

var that = this;

this._map.addEventListener("zoomend",

function() {

that._redraw()

});

this._map.addEventListener("moveend",

function() {

that._redraw()

});

var mkrs = opts["markers"];

isArray(mkrs) && this.addMarkers(mkrs)

};

MarkerClusterer.prototype.addMarkers = function(markers) {

for (var i = 0,

len = markers.length; i < len; i++) {

this._pushMarkerTo(markers[i])

}

this._createClusters()

};

MarkerClusterer.prototype._pushMarkerTo = function(marker) {

var index = indexOf(marker, this._markers);

if (index === -1) {

marker.isInCluster = false;

this._markers.push(marker)

}

};

MarkerClusterer.prototype.addMarker = function(marker) {

this._pushMarkerTo(marker);

this._createClusters()

};

MarkerClusterer.prototype._createClusters = function() {

var mapBounds = this._map.getBounds();

var extendedBounds = getExtendedBounds(this._map, mapBounds, this._gridSize);

for (var i = 0,

marker; marker = this._markers[i]; i++) {

if (!marker.isInCluster && extendedBounds.containsPoint(marker.getPosition())) {

this._addToClosestCluster(marker)

}

}

};

MarkerClusterer.prototype._addToClosestCluster = function(marker) {

var distance = 4000000;

var clusterToAddTo = null;

var position = marker.getPosition();

for (var i = 0,

cluster; cluster = this._clusters[i]; i++) {

var center = cluster.getCenter();

if (center) {

var d = this._map.getDistance(center, marker.getPosition());

if (d < distance) {

distance = d;

clusterToAddTo = cluster

}

}

}

if (clusterToAddTo && clusterToAddTo.isMarkerInClusterBounds(marker)) {

clusterToAddTo.addMarker(marker)

} else {

var cluster = new Cluster(this);

cluster.addMarker(marker);

this._clusters.push(cluster)

}

};

MarkerClusterer.prototype._clearLastClusters = function() {

for (var i = 0,

cluster; cluster = this._clusters[i]; i++) {

cluster.remove()

}

this._clusters = [];

this._removeMarkersFromCluster()

};

MarkerClusterer.prototype._removeMarkersFromCluster = function() {

for (var i = 0,

marker; marker = this._markers[i]; i++) {

marker.isInCluster = false

}

};

MarkerClusterer.prototype._removeMarkersFromMap = function() {

for (var i = 0,

marker; marker = this._markers[i]; i++) {

marker.isInCluster = false;

tmplabel = marker.getLabel();

this._map.removeOverlay(marker);

marker.setLabel(tmplabel)

}

};

MarkerClusterer.prototype._removeMarker = function(marker) {

var index = indexOf(marker, this._markers);

if (index === -1) {

return false

}

tmplabel = marker.getLabel();

this._map.removeOverlay(marker);

marker.setLabel(tmplabel);

this._markers.splice(index, 1);

return true

};

MarkerClusterer.prototype.removeMarker = function(marker) {

var success = this._removeMarker(marker);

if (success) {

this._clearLastClusters();

this._createClusters()

}

return success

};

MarkerClusterer.prototype.removeMarkers = function(markers) {

var success = false;

for (var i = 0; i < markers.length; i++) {

var r = this._removeMarker(markers[i]);

success = success || r

}

if (success) {

this._clearLastClusters();

this._createClusters()

}

return success

};

MarkerClusterer.prototype.clearMarkers = function() {

this._clearLastClusters();

this._removeMarkersFromMap();

this._markers = []

};

MarkerClusterer.prototype._redraw = function() {

this._clearLastClusters();

this._createClusters()

};

MarkerClusterer.prototype.getGridSize = function() {

return this._gridSize

};

MarkerClusterer.prototype.setGridSize = function(size) {

this._gridSize = size;

this._redraw()

};

MarkerClusterer.prototype.getMaxZoom = function() {

return this._maxZoom

};

MarkerClusterer.prototype.setMaxZoom = function(maxZoom) {

this._maxZoom = maxZoom;

this._redraw()

};

MarkerClusterer.prototype.getStyles = function() {

return this._styles

};

MarkerClusterer.prototype.setStyles = function(styles) {

this._styles = styles;

this._redraw()

};

MarkerClusterer.prototype.getMinClusterSize = function() {

return this._minClusterSize

};

MarkerClusterer.prototype.setMinClusterSize = function(size) {

this._minClusterSize = size;

this._redraw()

};

MarkerClusterer.prototype.isAverageCenter = function() {

return this._isAverageCenter

};

MarkerClusterer.prototype.getMap = function() {

return this._map

};

MarkerClusterer.prototype.getMarkers = function() {

return this._markers

};

MarkerClusterer.prototype.getClustersCount = function() {

var count = 0;

for (var i = 0,

cluster; cluster = this._clusters[i]; i++) {

cluster.isReal() && count++

}

return count

};

function Cluster(markerClusterer) {

this._markerClusterer = markerClusterer;

this._map = markerClusterer.getMap();

this._minClusterSize = markerClusterer.getMinClusterSize();

this._isAverageCenter = markerClusterer.isAverageCenter();

this._center = null;

this._markers = [];

this._gridBounds = null;

this._isReal = false;

this._clusterMarker = new BMapLib.TextIconOverlay(this._center, this._markers.length, {

"styles": this._markerClusterer.getStyles()

})

}

Cluster.prototype.addMarker = function(marker) {

if (this.isMarkerInCluster(marker)) {

return false

}

if (!this._center) {

this._center = marker.getPosition();

this.updateGridBounds()

} else {

if (this._isAverageCenter) {

var l = this._markers.length + 1;

var lat = (this._center.lat * (l - 1) + marker.getPosition().lat) / l;

var lng = (this._center.lng * (l - 1) + marker.getPosition().lng) / l;

this._center = new BMap.Point(lng, lat);

this.updateGridBounds()

}

}

marker.isInCluster = true;

this._markers.push(marker);

var len = this._markers.length;

if (len < this._minClusterSize) {

this._map.addOverlay(marker);

return true

} else if (len === this._minClusterSize) {

for (var i = 0; i < len; i++) {

tmplabel = this._markers[i].getLabel();

this._markers[i].getMap() && this._map.removeOverlay(this._markers[i]);

this._markers[i].setLabel(tmplabel)

}

}

this._map.addOverlay(this._clusterMarker);

this._isReal = true;

this.updateClusterMarker();

return true

};

Cluster.prototype.isMarkerInCluster = function(marker) {

if (this._markers.indexOf) {

return this._markers.indexOf(marker) != -1

} else {

for (var i = 0,

m; m = this._markers[i]; i++) {

if (m === marker) {

return true

}

}

}

return false

};

Cluster.prototype.isMarkerInClusterBounds = function(marker) {

return this._gridBounds.containsPoint(marker.getPosition())

};

Cluster.prototype.isReal = function(marker) {

return this._isReal

};

Cluster.prototype.updateGridBounds = function() {

var bounds = new BMap.Bounds(this._center, this._center);

this._gridBounds = getExtendedBounds(this._map, bounds, this._markerClusterer.getGridSize())

};

Cluster.prototype.updateClusterMarker = function() {

if (this._map.getZoom() > this._markerClusterer.getMaxZoom()) {

this._clusterMarker && this._map.removeOverlay(this._clusterMarker);

for (var i = 0,

marker; marker = this._markers[i]; i++) {

this._map.addOverlay(marker)

}

return

}

if (this._markers.length < this._minClusterSize) {

this._clusterMarker.hide();

return

}

this._clusterMarker.setPosition(this._center);

this._clusterMarker.setText(this._markers.length);

var thatMap = this._map;

var thatBounds = this.getBounds();

this._clusterMarker.addEventListener("click",

function(event) {

thatMap.setViewport(thatBounds)

})

};

Cluster.prototype.remove = function() {

for (var i = 0,

m; m = this._markers[i]; i++) {

var tmplabel = this._markers[i].getLabel();

this._markers[i].getMap() && this._map.removeOverlay(this._markers[i]);

this._markers[i].setLabel(tmplabel)

}

this._map.removeOverlay(this._clusterMarker);

this._markers.length = 0;

delete this._markers

}

Cluster.prototype.getBounds = function() {

var bounds = new BMap.Bounds(this._center, this._center);

for (var i = 0,

marker; marker = this._markers[i]; i++) {

bounds.extend(marker.getPosition())

}

return bounds

};

Cluster.prototype.getCenter = function() {

return this._center

}

})();